Broadcast ranging messages for wlan rtt measurements

ABSTRACT

In one aspect, a method performed by an access point in a wireless local area network (WLAN), includes receiving a first ranging request message from a first device and monitoring for a second ranging request message from a second device on a channel of the WLAN. The first ranging request message includes a device identifier of the first device and the second ranging request message includes a device identifier of the second device. In response to receiving the second ranging request message, the access point combines the device identifier of the first device, first timing information associated with the first ranging request message, the device identifier of the second device, and second timing information associated with the second ranging request message into a single ranging response message. The access point then broadcasts the single ranging response message on the channel of the WLAN.

FIELD OF DISCLOSURE

Aspects of this disclosure relate generally to wireless communications,and more particularly to wireless local area network (WLAN) access point(AP) positioning and navigation systems.

BACKGROUND

Wireless communication systems are widely deployed to provide varioustypes of communication content, such as voice, data, and so on. Typicalwireless communication systems are multiple-access systems capable ofsupporting communication with multiple users by sharing available systemresources (e.g., bandwidth, transmit power, etc.). One class of suchmultiple-access systems is generally referred to as wireless locationarea networks (WLANs), such as “Wi-Fi,” and includes different membersof the Institute of Electrical and Electronics Engineers (IEEE) 802.11wireless protocol family. Generally, a Wi-Fi communication system cansimultaneously support communication for multiple wireless devices, suchas wireless stations (STAs). Each STA communicates with one or moreaccess points (APs) via transmissions on the downlink and the uplink.The downlink (DL) refers to the communication link from the APs to theSTAs, and the uplink (UL) refers to the communication link from the STAsto the APs.

Modern navigation systems have typically used satellite-based globalpositioning system (GPS) for position determination. However, the recentproliferation of WLAN (e.g., Wi-Fi) access points has made it possiblefor navigation systems to use these access points for positiondetermination, especially in urban areas where there is usually largeconcentration of WLAN access points. WLAN navigation systems can beadvantageous over GPS navigation systems because of limitations of GPSsignal coverage. For example, while GPS signals may not be readilyavailable inside a shopping mall, wireless signals generated by WLANaccess points inside the shopping mall would be more readily detectableby a STA.

More specifically, for WLAN navigation systems, the locations of theWLAN access points are used as reference points from which well-knowntrilateration techniques can determine the location (e.g., absolutelocation and/or relative location) of a wireless device (e.g., aWi-Fi-enabled cell phone, laptop, or tablet computer). The wirelessdevice can use the round trip time (RTT) of signals transmitted to andfrom the access points to calculate the distances between the wirelessdevice and the access points. Once these distances are calculated, thelocation of the wireless device can be estimated using trilaterationtechniques.

Conventional RTT techniques used to determine the distances between thewireless device and WLAN access points, are typically performed based ona peer-to-peer messaging protocol. Thus, the wireless device needs toknow which APs are in proximity to the wireless device in order toexchange peer-to-peer messages in these conventional RTT techniques. Forexample, the wireless device typically first performs a discovery scanto determine which APs are present on each channel of the WLAN.Alternatively, some location/venue specific databases may be used todetermine the APs in the proximity of the wireless device. Once thewireless device has knowledge of which APs are present and on whichchannels, the wireless device then exchanges messages with each knownAP, performing RTT measurements, one AP at a time. However, as WLANpositioning solutions require more and more precision, the wirelessdevice may be required to perform more frequent RTT measurements, withmany access points in its vicinity. This high periodicity of discoveryscans and many peer-to-peer RTT measurements can cause several problemsin the WLAN. For example, current 802.11 connectivity solutions are notdesigned for such high periodicity solutions, because each discoveryscan and RTT measurement is a disruption to the high speed datacapabilities of the WLAN. In addition, the increased periodicity ofdiscovery scans and peer-to-peer RTT measurements can adversely increasethe power consumption of the wireless device. Additionally, in thescenarios where there are many mobile devices doing similar operations(for example in crowded stadiums, where many mobile devices may beconcurrently trying to perform Location Based Services), the RTTRequests from many mobile devices may collide with one another, makingthe WLAN connectivity problems worse.

SUMMARY

Aspects of the present disclosure include a method, a device, an accesspoint, and a computer-readable medium for assisting or otherwiseperforming RTT measurements in a WLAN utilizing one or more broadcastranging messages.

For example, in one aspect, a method performed by an access point in awireless local area network (WLAN), includes receiving a first rangingrequest message from a first device and monitoring for a second rangingrequest message from a second device on a channel of the WLAN. The firstranging request message includes a device identifier of the first deviceand the second ranging request message includes a device identifier ofthe second device. In response to receiving the second ranging requestmessage, the access point combines the device identifier of the firstdevice, first timing information associated with the first rangingrequest message, the device identifier of the second device, and secondtiming information associated with the second ranging request messageinto a single ranging response message. The access point then broadcaststhe single ranging response message on the channel of the WLAN.

In another aspect, an access point for use in a wireless local areanetwork (WLAN), includes at least one processor and at least one memorycoupled to the at least one processor. The at least one processor andthe at least one memory are configured to direct the access point to:(i) receive a first ranging request message from a first device on achannel of the WLAN, wherein the first ranging request message includesa device identifier of the first device; (ii) monitor the channel of theWLAN for a second ranging request message from a second device, whereinthe second ranging request message includes a device identifier of thesecond device; (iii) in response to receiving the second ranging requestmessage from the second device, combine the device identifier of thefirst device, first timing information associated with the first rangingrequest message, the device identifier of the second device, and secondtiming information associated with the second ranging request messageinto a single ranging response message, wherein the first and secondtiming information are for determining round trip time (RTT)measurements, by the first and second devices, respectively; and (iv)broadcast the single ranging response message on the channel of theWLAN.

In yet another aspect, an access point for use in a wireless local areanetwork (WLAN) includes means for receiving, by the access point, afirst ranging request message from a first device on a channel of theWLAN, wherein the first ranging request message includes a deviceidentifier of the first device. The access point also includes means formonitoring the channel of the WLAN for a second ranging request messagefrom a second device, wherein the second ranging request messageincludes a device identifier of the second device. Also included in theaccess point are means for combining, by the access point, the deviceidentifier of the first device, first timing information associated withthe first ranging request message, the device identifier of the seconddevice, and second timing information associated with the second rangingrequest message into a single ranging response message in response toreceiving the second ranging request message from the second device. Thefirst and second timing information are for determining round trip time(RTT) measurements, by the first and second devices, respectively. Theaccess point further includes means for broadcasting, by the accesspoint, the single ranging response message on the channel of the WLAN.

In another aspect, a non-transitory computer-readable medium includesprogram code stored thereon. The program code includes instructions todirect an access point to: (i) receive a first ranging request messagefrom a first device on a channel of the WLAN, wherein the first rangingrequest message includes a device identifier of the first device; (ii)monitor the channel of the WLAN for a second ranging request messagefrom a second device, wherein the second ranging request messageincludes a device identifier of the second device; (iii) in response toreceiving the second ranging request message, combine the deviceidentifier of the first device, first timing information associated withthe first ranging request message, the device identifier of the seconddevice, and second timing information associated with the second rangingrequest message into a single ranging response message, wherein thefirst and second timing information are for determining round trip time(RTT) measurements, by the first and second devices, respectively; and(iv) broadcast the single ranging response message on the channel of theWLAN.

In yet another aspect, a method performed by a device in a wirelesslocal area network (WLAN) includes transmitting, by the device, a firstranging request message on a channel of the WLAN, wherein the firstranging request message includes a device identifier of the device. Themethod also includes receiving, by the device, a first broadcast rangingresponse message broadcast on the channel by a first access point of theWLAN in response to the first ranging request message. The firstbroadcast ranging response message includes: the device identifier ofthe device, first timing information associated with the first rangingrequest message, a device identifier of a second device in the WLAN, andsecond timing information associated with a second ranging requestmessage transmitted on the channel of the WLAN by the second device. Themethod also includes determining a round trip time (RTT) measurement forthe first access point based on the first ranging request message andthe first timing information included in the first broadcast rangingresponse message.

In another aspect, device for use in a wireless local area network(WLAN), includes at least one processor and at least one memory coupledto the at least one processor. The at least one processor and the atleast one memory are configured to direct the device to: (i) transmit afirst ranging request message on a channel of the WLAN, wherein thefirst ranging request message includes a device identifier of thedevice; (ii) receive a first broadcast ranging response messagebroadcast on the channel by a first access point of the WLAN in responseto the first ranging request message, where the first broadcast rangingresponse message includes: the device identifier of the device, firsttiming information associated with the first ranging request message, adevice identifier of a second device in the WLAN, and second timinginformation associated with a second ranging request message transmittedon the channel of the WLAN by the second device; and (iii) determine around trip time (RTT) measurement for the first access point based onthe first ranging request message and the first timing informationincluded in the first broadcast ranging response message.

In yet another aspect, a device for use in a wireless local area network(WLAN) includes means for transmitting, by the device, a first rangingrequest message on a channel of the WLAN, wherein the first rangingrequest message includes a device identifier of the device. The devicealso includes means for receiving, by the device, a first broadcastranging response message broadcast on the channel by a first accesspoint of the WLAN in response to the first ranging request message. Thefirst broadcast ranging response message includes: the device identifierof the device, first timing information associated with the firstranging request message, a device identifier of a second device in theWLAN, and second timing information associated with a second rangingrequest message transmitted on the channel of the WLAN by the seconddevice. The device also includes means for determining a round trip time(RTT) measurement for the first access point based on the first rangingrequest message and the first timing information included in the firstbroadcast ranging response message.

In another aspect, a non-transitory computer-readable medium includesprogram code stored thereon. The program code includes instructions todirect device in a wireless local area network (WLAN) to: (i) transmit afirst ranging request message on a channel of the WLAN, wherein thefirst ranging request message includes a device identifier of thedevice; (ii) receive a first broadcast ranging response messagebroadcast on the channel by a first access point of the WLAN in responseto the first ranging request message, where the first broadcast rangingresponse message includes: the device identifier of the device, firsttiming information associated with the first ranging request message, adevice identifier of a second device in the WLAN, and second timinginformation associated with a second ranging request message transmittedon the channel of the WLAN by the second device; and (iii) determine around trip time (RTT) measurement for the first access point based onthe first ranging request message and the first timing informationincluded in the first broadcast ranging response message.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are presented to aid in the description ofvarious aspects of the disclosure and are provided solely forillustration of the aspects and not limitation thereof.

FIG. 1 illustrates an example wireless network employing a Wi-Fiprotocol.

FIG. 2A is a flowchart illustrating a process of transmitting a firstranging request message in a WLAN for determining RTT measurements by awireless device.

FIG. 2B is a diagram illustrating an example first broadcast rangingresponse message.

FIG. 3 is a flowchart illustrating a process of broadcasting rangingrequest messages in a WLAN for determining RTT measurements by awireless device.

FIG. 4 is a flowchart illustrating a process of receiving first andsecond ranging request messages at an access point of a WLAN.

FIG. 5 is a flowchart illustrating a process of broadcasting a rangingresponse message on a channel of a WLAN.

FIG. 6 is a call flow procedure illustrating the broadcasting of rangingmessages in a WLAN.

FIG. 7 is a simplified block diagram of several sample aspects ofcomponents that may be employed in an apparatus and configured tosupport communication as taught herein.

FIGS. 8 and 9 are other simplified block diagrams of several sampleaspects of apparatuses configured to support communication as taughtherein.

FIG. 10 is a call flow procedure illustrating the unicasting of rangingrequest messages in a WLAN.

DETAILED DESCRIPTION

More specific aspects of the disclosure are provided in the followingdescription and related drawings directed to various examples providedfor illustration purposes. Alternate aspects may be devised withoutdeparting from the scope of the disclosure. Additionally, well-knownaspects of the disclosure may not be described in detail or may beomitted so as not to obscure more relevant details.

Those of skill in the art will appreciate that the information andsignals described below may be represented using any of a variety ofdifferent technologies and techniques. For example, data, instructions,commands, information, signals, bits, symbols, and chips that may bereferenced throughout the description below may be represented byvoltages, currents, electromagnetic waves, magnetic fields or particles,optical fields or particles, or any combination thereof, depending inpart on the particular application, in part on the desired design, inpart on the corresponding technology, etc.

Further, many aspects are described in terms of sequences of actions tobe performed by, for example, elements of a computing device. It will berecognized that various actions described herein can be performed byspecific circuits (e.g., Application Specific Integrated Circuits(ASICs)), by program instructions being executed by one or moreprocessors, or by a combination of both. In addition, for each of theaspects described herein, the corresponding form of any such aspect maybe implemented as, for example, “logic configured to” perform thedescribed action.

FIG. 1 illustrates an example wireless network 100. As shown, thewireless network 100, which may also be referred to herein as a BasicService Set (BSS), is formed from several wireless nodes, including oneor more Access Points (APs) 110A and 110B and a plurality of subscriberstations (STAs) 120A and 120B. Each wireless node is generally capableof receiving and/or transmitting. The wireless network 100 may supportany number of APs 110A and 110B distributed throughout a geographicregion to provide coverage for the STAs 120A and 120B. For simplicity,only two APs 110A and 110B are shown in FIG. 1, providing coordinationand control among the STAs 120A and 120B, as well as access to other APsor other networks (e.g., the Internet) via a backhaul connection 130.However, in other examples, the wireless network 100 may include many(more than two) APs, including several APs operating on the same WLANchannel and several other APs operating on different WLAN channels.

The APs 110A and 110B are generally fixed entities that provide backhaulservices to the STAs 120A and 120B in their geographic region ofcoverage. However, the APs 110A and 110B may be mobile in someapplications (e.g., a mobile device serving as a wireless hotspot forother devices). The STAs 120A and 120B may be fixed or mobile. Examplesof STAs 120A and 120B include a telephone (e.g., cellular telephone), alaptop computer, a desktop computer, a personal digital assistant (PDA),a digital audio player (e.g., MP3 player), a camera, a game console, adisplay device, or any other suitable wireless node. The wirelessnetwork 100 may be referred to as a wireless local area network (WLAN),and may employ a variety of widely used networking protocols tointerconnect nearby devices. In general, these networking protocols maybe referred to as “Wi-Fi,” including any member of the Institute ofElectrical and Electronics Engineers (IEEE) 802.11 wireless protocolfamily.

As discussed above, conventional discovery scan and peer-to-peer RTTmeasurements may disrupt high speed data capabilities of the WLAN aswell as adversely impact the power consumption of the wireless device.Accordingly, the different entities shown in FIG. 1 may be variouslyconfigured in accordance with the teachings herein to provide orotherwise support the broadcasting of ranging messages in wirelessnetwork 100 for determining RTT measurements. In some aspects, thebroadcasting of ranging messages provides for a reduction in thetimeline associated with performing RTT measurements on each Wi-Fichannel. Thus, as shown in FIG. 1, the STA 120A may include a rangingmessage manager 122 for broadcasting a ranging request message to allAPs on a channel of the WLAN, while AP 110A may include a rangingmessage manager 112 that monitors the channel for such broadcast rangingrequest messages. These and other aspects will be described in moredetail below.

FIG. 2A is a flowchart illustrating a process 200 of transmitting afirst ranging request message in a WLAN for determining RTT measurementsby a wireless device. Process 200 is one possible process performed by awireless device (e.g., the STA 120A under direction of ranging messagemanager 122). In process block 210, STA 120A transmits a first rangingrequest message (e.g., a probe) on a channel of the WLAN (e.g., wirelessnetwork 100). The first ranging request message transmitted by STA 120Amay include a device identifier of the wireless device, such as a mediaaccess control (MAC) address of STA 120A.

In one embodiment, the STA 120A broadcasts the first ranging requestmessage on the channel of the WLAN without a priori knowledge of whichof the APs (110A or 110B) are available on the first channel of theWLAN. That is, the STA 120A may broadcast the first ranging requestmessage without the need to know the MAC address of any APs (e.g., AP110A and AP 110B). As will be discussed below with reference to FIGS. 4and 5, one or more APs operating on this channel of the WLAN may receivethe transmitted ranging request message and generate a ranging responsemessage (e.g., a beacon) in response thereto. Thus, in process block220, STA 120A receives a first broadcast ranging response message thatis sent by a first AP (e.g., AP 110A) of the WLAN (e.g. wireless network100). In one aspect the first broadcast ranging response message isgenerated by the AP 110A in response to several ranging request messagestransmitted on the channel of the WLAN by several wireless devices. Forexample, both STA 120A and STA 120B may each generate and transmit aranging request message to AP 110A. In response to receiving multipleranging request messages, the AP 110A may combine relevant timinginformation associated with each of the received ranging requestmessages into a single broadcast ranging response message that isbroadcast back to STA 120A and STA 120B on the channel of the WLAN. Forexample, FIG. 2B is a diagram illustrating a first broadcast rangingresponse message 232. The illustrated example of the first broadcastranging response message 232 includes a device identifier 234 of a firstdevice (e.g., STA 120A), timing information associated with a firstranging request message transmitted on the channel by the first device,a device identifier 238 of a second device (e.g., STA 120B), and timinginformation associated with a second ranging request message transmittedon the channel by the second device. The first broadcast rangingresponse message 232 may include further device identifiers 242 andcorresponding timing information 244 for each of a plurality of rangingrequest messages received at the AP 110A. In one aspect, the deviceidentifiers 234 and 238 are the MAC addresses of the correspondingwireless devices (e.g., STA 120A and STA 120B) that transmitted aranging request message to AP 110A. Furthermore, the timing information236 and 240 may include a time-stamp indicating a time that therespective ranging request message was received at the AP 110A.

Returning now back to FIG. 2A, process 200 next includes process block230, where STA 120A determines a round trip time (RTT) measurement forthe first access point (e.g., AP 110A) based on the first rangingrequest message (e.g., a time that the first ranging request message wastransmitted on the channel of the WLAN by STA 120A) and the timinginformation (e.g., timing information 236) included in the firstbroadcast ranging response message 232. As mentioned above, the firstbroadcast ranging response message 232 includes several deviceidentifiers and associated timing information. Thus, the STA 120A mayretrieve the relevant timing information from the first broadcastranging response message 232 based on the known device identifier (e.g.,MAC address) of the STA 120A. That is, STA 120A may be configured toextract, from the first broadcast ranging response message 232, timinginformation related to only the ranging request message broadcast by STA120A, itself, based on the MAC address of STA 120A.

As will be discussed in more detail with reference to process 300 ofFIG. 3, the illustrated process blocks 210, 220, and 230, ofbroadcasting, monitoring, and determining, respectively, may be repeatedby STA 120A for each of a plurality of channels included in the WLAN.

FIG. 3 is a flowchart illustrating a process 300 of broadcasting rangingrequest messages in a WLAN for determining RTT measurements by awireless device. Process 300 is one possible process performed by awireless device (e.g., the STA 120A under direction of ranging messagemanager 122). In process block 310, STA 120A selects a channel of theWLAN. As discussed above, once the STA 120A broadcasts a ranging requestmessage, the STA 120A then monitors the respective channel for rangingresponse messages. In one embodiment, the STA 120A monitors the channelfor a wait time period. In one aspect, the wait time period provides atime period to allow for multiple APs to respond to the ranging requestmessage since different APs may have differing delays and/or congestionissues. Furthermore, APs may randomize the time at which they broadcasttheir ranging response messages so as to avoid collisions with oneanother. Thus, the wait time period may further allow for thesebroadcast ranging response messages to be spread out over time. In oneembodiment, the wait time period utilized by STA 120A is fixed. Inanother embodiment, the wait time period is variable. Thus, process 300includes optional process block 320 of varying the wait time periodbased, in part, on an activity level of the selected channel. In denseAP environments (e.g., WLANs with many APs operating on the samechannel), the activity level of a selected channel may be high and thus,the response time of one or more of the APs may be slow. Accordingly,process block 320 may include determining the activity level of theselected channel and comparing the activity level with one or moreactivity level thresholds to vary the wait time period. In one aspect,process block 320 includes increasing the wait time period if theactivity level of the selected channel is above or exceeds an activitylevel threshold indicating a higher level of activity on the selectedchannel. Increasing the wait time period for active channels may ensurethat each AP is given enough time to generate and broadcast a rangingresponse message. Similarly, decreasing the wait time period of lessactive channels may allow the STA 120A to complete the RTT measurementsquicker with less wasted time.

Continuing now with process 300, with the wait time period set, next inprocess block 330, STA 120A broadcasts the ranging request message onthe selected channel. In process block 340, STA 120A monitors theselected channel for broadcast ranging response messages. As discussedabove, the ranging request message is a broadcast message sent to everyAP operating on the selected channel. Thus, monitoring the selectedchannel may include receiving multiple broadcast ranging responsemessages. For example, STA 120A may receive a first broadcast rangingresponse message 232 on the selected channel from AP 110A and may alsoreceive another first broadcast ranging response message 232 on theselected channel from AP 110B.

Next, in decision block 350, STA 120A determines whether the end of thewait time period has been reached. If not, process 300 returns toprocess block 340 where STA 120A continues to monitor the selectedchannel for further broadcast ranging response messages. If, in decisionblock 350, it is determined that the end of the wait time period hasbeen reached, then process 300 proceeds to process block 360 where STA120A determines the RTT measurements based on the received broadcastranging response messages. For example, the STA 120A may determine afirst RTT measurement based on a first ranging response message 232received from AP 110A and may also determine a second RTT measurementbased on a first ranging response message 232 received from AP 110B. Thefirst RTT measurement may be representative of a distance between STA120A and AP 110A, while the second RTT measurement may be representativeof a distance between STA 120A and AP 110B.

In decision block 370, STA 120A determines whether RTT measurements havebeen completed for all channels of the WLAN. If so, process 300 ends. Ifnot, process block 380 selects a next channel of the WLAN and process300 returns to process block 320.

FIG. 4 is a flowchart illustrating a process 400 of receiving first andsecond ranging request messages at an access point of a WLAN. Process400 is one possible process performed by a base station (e.g., the AP110A and/or AP 110B under direction of ranging message manager 112). Ina process block 410, AP 110A receives a first ranging request messagefrom a first device (e.g., STA 120A) on a channel of the WLAN, where thefirst ranging request message includes a device identifier (e.g., MACaddress) of the first device. In a process block 420, AP 110A monitorsthe channel of the WLAN for a second ranging request message from asecond device (e.g., STA 120B), where the second ranging request messageincludes a device identifier (e.g., MAC address) of the second device.

Next, in process block 430, in response to receiving the second rangingrequest message from the second device, the AP 110A combines the deviceidentifier of the first device, first timing information associated withthe first ranging request message, the device identifier of the seconddevice, and second timing information associated with the second rangingrequest message into a single broadcast ranging response message, suchas broadcast ranging response message 232 of FIG. 2B. As discussedabove, the timing information may be time stamps corresponding to whenthe respective ranging request messages were received at AP 110A and thedevice identifiers may be the MAC addresses of the respective first andsecond devices (e.g., STA 120A and STA 120B). The AP 110A thenbroadcasts the single ranging response message on the channel of theWLAN (i.e., process block 440). In one aspect, the AP 110A may receive aranging request message from only one device (e.g., STA 120A) of theWLAN. That is, the AP 110A may not receive any additional rangingrequest messages other than the first ranging request message receivedfrom the first device (e.g., STA 120A). Thus, in this example, thesingle ranging response message broadcast in process block 440 mayinclude the device identifier only of the first device and timinginformation associated only with the ranging request message receivedfrom the first device.

FIG. 5 is a flowchart illustrating a process 500 of broadcasting aranging response message by an access point of a WLAN. Process 500 isone possible process performed by a base station (e.g., the AP 110Aand/or AP 110B under direction of ranging message manager 112). In oneembodiment, an AP may include a response time period that represents anamount of time that the AP may wait upon receiving a ranging requestmessage before sending a corresponding ranging response message. Theresponse time period may allow the AP to respond to multiple rangingrequest messages received from multiple mobile devices, by broadcastinga combined single ranging response message (e.g., broadcast rangingresponse message 232) in response to all of the ranging request messagesreceived during the response time period. In one embodiment, theresponse time period is fixed. However, as discussed above, differentchannels of the WLAN may experience different levels of activity due totraffic, differing delays and/or congestion issues. Thus, in anotherembodiment, the response time period is variable, where process 500includes optional process block 510 of varying and/or randomizing theresponse time period based, in part, on a determined activity level ofthe channel. In one aspect, the AP 110A and/or AP 110B may increase theresponse time period in response to the activity level of the firstchannel being above a first activity threshold that indicates a higherlevel of activity on the first channel. Similarly, AP 110A and/or AP110B may decrease the response time period for channels that areexperiencing a lower level of activity (e.g., less traffic). Processblock 510 may also include randomizing the response time period so as toreduce interference with other ranging response messages broadcast byother access points in the WLAN. For example, AP 110A, throughrandomization, may vary the response time period by a first amount,where AP 110B, again through randomization, may vary its response timeperiod by a second amount, such that the ranging response messagebroadcast by AP 110A occurs at a different time than the broadcasting ofa ranging response message by AP 110B.

With the response time period set in process block 510, process 500begins monitoring a channel of the WLAN for ranging request messages,where in process block 520 a first ranging response message is receivedat the AP on the first channel. Once the first ranging response messageis received at the AP (e.g., AP 110A and/or AP 110B), process block 530begins the response time period. Next, in process block 540 and decisionblock 550, the AP continues monitoring the first channel of the WLAN foradditional ranging request messages until the end of the response timeperiod is reached.

In one embodiment, the ranging request messages received at the AP, eachinclude a MAC address of the wireless device that broadcast the rangingrequest message. Process block 560 thus includes combining these MACaddresses and related timing information for the receiving rangingrequest messages into a single ranging response message. In oneembodiment, the ranging response message includes, for each rangingrequest message received, (1) the MAC address of the device thatbroadcast the ranging request message, (2) a first time-stamp indicatinga time that the ranging request message was received at the AP, and (3)a second time-stamp indicating a time that the AP is sending the rangingresponse message. Including the second time-stamp in the rangingresponse message may allow the wireless device to compensate orotherwise account for the delay associated with the response time periodutilized at the AP. As will be discussed in more detail below, ratherthan include the second time-stamp in the ranging response message, theAP may optionally generate and transmit a second ranging responsemessage that includes the second time-stamp indicating the time that thefirst ranging response message was broadcast on the channel of the WLAN.

Next, in process block 570, the AP 110A and/or AP 110B broadcasts theranging response message on the first channel. In one aspect, the AP110A may receive a ranging request message from only one device (e.g.,STA 120A) of the WLAN during the response time period. Thus, in thisexample, the single ranging response message broadcast in process block570 may include the device identifier only of the first device andtiming information associated only with the ranging request messagereceived from the first device in process block 520.

FIG. 6 is a call flow procedure 600 illustrating the broadcasting ofranging messages in a WLAN. At time T1, the STA1 broadcasts a firstranging request message 610. In one embodiment, the broadcast rangingrequest message 610 is sent using a non-HT duplicate PPDU so as to havethe widest bandwidth. At time T2, the AP1 receives the first rangingrequest message 610 and in response thereto, initiates the beginning ofa response time period 630 at time T2. During the response time period630, STA2 also broadcasts a ranging request message (i.e., secondranging request message 640), but at time T3. The second broadcastranging request message 640 is received at the AP1 at time T4. The AP1then continues to monitor the channel for additional ranging requestmessages until the expiration of the response time period 630 at timeT5. At time T5, the AP1 broadcasts the first broadcast ranging responsemessage 660. The broadcast ranging response message 660 includes the MACaddress of STA1, an indication of time T2 (i.e., time that AP1 receivedthe first ranging request message 610), the MAC address of STA2, and anindication of time T4 (i.e., the time that AP1 received the secondranging request message 640). The broadcast ranging response message 660may also include a Neighbor Report. In one embodiment, the firstbroadcast ranging response message 660 contains all the necessaryinformation for STA1 and STA2 to do RTT. The illustrated example of FIG.6 shows the first broadcast ranging response message 660 being receivedby STA1 at time T6 and by STA2 at time T7.

At time T8, a second broadcast ranging response message 670 is broadcastby the AP1. The second broadcast ranging response message 660 includesan indication (e.g., time stamp) of time T5 (i.e., the time that thefirst broadcast ranging response message 660 was sent by the AP1). Attime T9, the STA1 receives the second broadcast ranging response message670 and can then begin determining the RTT measurements. At time T10,the STA2 receives the same second broadcast ranging response message 670and can begin determining its own RTT measurements. Note that if thesecond broadcast ranging response message 670 is not received by eitherSTA1 or STA2, another Broadcast Ranging Request Message could be sent byeither STA to indicate that the second broadcast ranging responsemessage 670 should be retransmitted by the AP 1.

FIG. 6 further illustrates a second access point AP2 that receives thebroadcast ranging request messages 610 and 640. The second access pointAP2 is configured similarly to AP1 and may include initiating its ownresponse time period 630 in response to receiving broadcast rangingrequest message 610, and may also generate its own first and secondbroadcast ranging response messages 660 and/or 670, similar to thatdescribed above with reference AP1.

In one embodiment of a wireless device in accordance with the teachingsherein, the access point includes a Wi-Fi stack and LTE stack that areintegrated on a single processor. However, in other embodiments, awireless device in accordance with the teachings herein may include aWi-Fi stack integrated into a single processor along with any otherprotocol stack that has periodic activity, such as WCDMA and CDMA.

FIG. 7 illustrates several sample components (represented bycorresponding blocks) that may be incorporated into an apparatus 702, anapparatus 704, and an apparatus 706 (corresponding to, for example, auser device, a base station, and a network entity, respectively) tosupport the broadcast ranging message operations as taught herein. Itwill be appreciated that these components may be implemented indifferent types of apparatuses in different implementations (e.g., in anASIC, in an SoC, etc.). The illustrated components may also beincorporated into other apparatuses in a communication system. Forexample, other apparatuses in a system may include components similar tothose described to provide similar functionality. Also, a givenapparatus may contain one or more of the components. For example, anapparatus may include multiple transceiver components that enable theapparatus to operate on multiple carriers and/or communicate viadifferent technologies.

The apparatus 702 and the apparatus 704 each include at least onewireless communication device (represented by the communication devices708 and 714 (and the communication device 720 if the apparatus 704 is arelay)) for communicating with other nodes via at least one designatedradio access technology (RAT). Each communication device 708 includes atleast one transmitter (represented by the transmitter 710) fortransmitting and encoding signals (e.g., messages, indications,information, and so on) and at least one receiver (represented by thereceiver 712) for receiving and decoding signals (e.g., messages,indications, information, pilots, and so on). Similarly, eachcommunication device 714 includes at least one transmitter (representedby the transmitter 716) for transmitting signals (e.g., messages,indications, information, pilots, and so on) and at least one receiver(represented by the receiver 718) for receiving signals (e.g., messages,indications, information, and so on). If the apparatus 704 is a relaystation, each communication device 720 may include at least onetransmitter (represented by the transmitter 722) for transmittingsignals (e.g., messages, indications, information, pilots, and so on)and at least one receiver (represented by the receiver 724) forreceiving signals (e.g., messages, indications, information, and so on).

A transmitter and a receiver may comprise an integrated device (e.g.,embodied as a transmitter circuit and a receiver circuit of a singlecommunication device) in some implementations, may comprise a separatetransmitter device and a separate receiver device in someimplementations, or may be embodied in other ways in otherimplementations. A wireless communication device (e.g., one of multiplewireless communication devices) of the apparatus 704 may also comprise aNetwork Listen Module (NLM) or the like for performing variousmeasurements.

The apparatus 706 (and the apparatus 704 if it is not a relay station)includes at least one communication device (represented by thecommunication device 726 and, optionally, 720) for communicating withother nodes. For example, the communication device 726 may comprise anetwork interface that is configured to communicate with one or morenetwork entities via a wire-based or wireless backhaul. In some aspects,the communication device 726 may be implemented as a transceiverconfigured to support wire-based or wireless signal communication. Thiscommunication may involve, for example, sending and receiving: messages,parameters, or other types of information. Accordingly, in the exampleof FIG. 7, the communication device 726 is shown as comprising atransmitter 728 and a receiver 730. Similarly, if the apparatus 704 isnot a relay station, the communication device 720 may comprise a networkinterface that is configured to communicate with one or more networkentities via a wire-based or wireless backhaul. As with thecommunication device 726, the communication device 8720 is shown ascomprising a transmitter 722 and a receiver 724.

The apparatuses 702, 704, and 706 also include other components that maybe used in conjunction with the broadcast ranging message operations astaught herein. The apparatus 702 includes a processing system 732 forproviding functionality relating to, for example, the broadcasting of aranging request message, the monitoring of a channel of the WLAN forranging response messages, and the determining of RTT measurements, astaught herein and for providing other processing functionality. Theapparatus 704 includes a processing system 734 for providingfunctionality relating to, for example, the monitoring of a channel ofthe WLAN for ranging request messages, combining device identifiers andcorresponding timing information into a single ranging request message,and the broadcasting of the single ranging response message, as taughtherein and for providing other processing functionality. The apparatus706 includes a processing system 736 for providing functionalityrelating to, for example, optionally aiding apparatus 702 in thedetermining of the RTT measurements and for providing other processingfunctionality. The apparatuses 702, 704, and 706 include memorycomponents 738, 740, and 742 (e.g., each including a memory device),respectively, for maintaining information (e.g., information indicativeof reserved resources, thresholds, parameters, and so on). In addition,the apparatuses 702, 704, and 706 include user interface devices 744,746, and 748, respectively, for providing indications (e.g., audibleand/or visual indications) to a user and/or for receiving user input(e.g., upon user actuation of a sensing device such a keypad, a touchscreen, a microphone, and so on).

For convenience, the apparatuses 702, 704, and/or 706 are shown in FIG.7 as including various components that may be configured according tothe various examples described herein. It will be appreciated, however,that the illustrated blocks may have different functionality indifferent designs.

The components of FIG. 7 may be implemented in various ways. In someimplementations, the components of FIG. 7 may be implemented in one ormore circuits such as, for example, one or more processors and/or one ormore ASICs (which may include one or more processors). Here, eachcircuit may use and/or incorporate at least one memory component forstoring information or executable code used by the circuit to providethis functionality. For example, some or all of the functionalityrepresented by blocks 708, 732, 738, and 744 may be implemented byprocessor and memory component(s) of the apparatus 702 (e.g., byexecution of appropriate code and/or by appropriate configuration ofprocessor components). Similarly, some or all of the functionalityrepresented by blocks 714, 720, 734, 740, and 746 may be implemented byprocessor and memory component(s) of the apparatus 704 (e.g., byexecution of appropriate code and/or by appropriate configuration ofprocessor components). Also, some or all of the functionalityrepresented by blocks 726, 736, 742, and 748 may be implemented byprocessor and memory component(s) of the apparatus 706 (e.g., byexecution of appropriate code and/or by appropriate configuration ofprocessor components).

FIG. 8 illustrates an example base station apparatus 800 represented asa series of interrelated functional modules. Base station apparatus 800is one possible implementation of AP 110A, AP 110B, and/or apparatus704. A module for receiving a first ranging request message from a firstdevice on a channel of a WLAN 802 may correspond at least in someaspects to, for example, a communication device 714, as discussedherein. A module for monitoring the channel of the WLAN for a secondranging request message from a second device 804 may correspond at leastin some aspects to, for example, a communication device 714, asdiscussed herein. A module for combining the device identifier of thefirst device, timing information associated with the first rangingrequest message, the device identifier of the second device, and timinginformation associated with the second ranging request into a singleranging response message 806 may correspond, at least in some aspect to,for example, processing system 734 and/or memory component 740. A modulefor broadcasting the single ranging response message on the channel ofthe WLAN 808 may correspond at least in some aspects to, for example,communication device 714, as discussed herein.

FIG. 9 illustrates an example user device apparatus 900 represented as aseries of interrelated functional modules. User device apparatus 900 isone possible implementation of STA 120A, STA 120B, and/or apparatus 702.A module for transmitting a first ranging request message on a channelof a WLAN 902 may correspond at least in some aspects to, for example, acommunication device 708, as discussed herein. A module for receiving afirst broadcast ranging response message broadcast on the channel by anaccess point 904 may correspond at least in some aspects to, forexample, a communication device 708, as discussed herein. A module fordetermining an RTT measurement for each access point based on theranging request message and timing information included in the firstbroadcast ranging response message 906 may correspond at least in someaspects to, for example, a processing system 732 and/or memory component738, as discussed herein.

The functionality of the modules of FIGS. 8 and 9 may be implemented invarious ways consistent with the teachings herein. In some designs, thefunctionality of these modules may be implemented as one or moreelectrical components. In some designs, the functionality of theseblocks may be implemented as a processing system including one or moreprocessor components. In some designs, the functionality of thesemodules may be implemented using, for example, at least a portion of oneor more integrated circuits (e.g., an ASIC). As discussed herein, anintegrated circuit may include a processor, software, other relatedcomponents, or some combination thereof. Thus, the functionality ofdifferent modules may be implemented, for example, as different subsetsof an integrated circuit, as different subsets of a set of softwaremodules, or a combination thereof. Also, it will be appreciated that agiven subset (e.g., of an integrated circuit and/or of a set of softwaremodules) may provide at least a portion of the functionality for morethan one module.

In addition, the components and functions represented by FIGS. 8 and 9,as well as other components and functions described herein, may beimplemented using any suitable means. Such means also may beimplemented, at least in part, using corresponding structure as taughtherein. For example, the components described above in conjunction withthe “module for” components of FIGS. 8 and 9 also may correspond tosimilarly designated “means for” functionality. Thus, in some aspectsone or more of such means may be implemented using one or more ofprocessor components, integrated circuits, or other suitable structureas taught herein.

FIG. 10 is a call flow procedure illustrating the unicasting of rangingrequest messages in a WLAN incorporating the use of dialog tokens, aswell as follow-up dialog tokens. At time T1, having completed adiscovery of available APs, the STA1 unicasts a first ranging requestmessage 1010 that includes a non-zero Dialog Token DT1. In oneembodiment, the unicast ranging request message 1010 is sent using anon-HT duplicate PPDU so as to have the widest bandwidth. At time T2,the AP receives the first ranging request message 1010 and in responsethereto, sends an acknowledgement (Ack) message 1020 at time T3. Thus,the response time period 1030 begins at time T2. The STA1 receives theAck message 1020 at time T4. If, however, the Ack 1020 is not receivedby STA1, the STA1 may send a new ranging request message with a dialogtoken DT1=DT1+1. During the response time period 1030, STA2 alsounicasts a ranging request message (i.e., second ranging request message1040), but at time T5, with a non-zero Dialog Token DT2 that isindependent of the Dialog Token chosen by STA1. The second unicastranging request message 1040 is received at the AP at time T6 and an Ackmessage 1050 is sent by the AP at time T7. The Ack message 1050 isreceived by the STA2 at time T8. If, however, the Ack message 1050 isnot received by STA2, the STA2 shall send a new broadcast rangingrequest message with DT2=DT2+1. In one embodiment, the Ack message 1020and the Ack message 1050 are not broadcast messages, and are insteadunicast messages. The AP then continues to monitor the channel foradditional ranging request messages until the expiration of the responsetime period 1030 at time T9. At time T9, the AP broadcasts a firstbroadcast ranging response message 1060. The first broadcast rangingresponse message 1060 includes the MAC address of STA1, the Dialog TokenDT1, an indication of time T2 (i.e., time that AP received the firstranging request message 1010), an indication of T3 (i.e., time that APsent the first Ack message 1020), the MAC address of STA2, the DialogToken DT2, and an indication of time T6 (i.e., the time that AP receivedthe second ranging request message 1040), and an indication of time T7(i.e., the time that the AP sent the second Ack message 1050). The firstbroadcast ranging response message 1060 may also include a NeighborReport, a Dialog Token DT3 and a Follow Up Dialog Token set to 0 (toindicate it is the initial one). In one embodiment, the first broadcastranging response message 1060 contains all the necessary information forSTA1 and STA2 to do RTT. In an alternative embodiment, the firstbroadcast ranging response message 1060 could include a differencebetween time T3 and time T2 (e.g., T3-T2) as well as a differencebetween time T7 and time T6 (e.g., T7-T6) so as to save bits. At timeT12, a second broadcast ranging response message 1070 is broadcast thatincludes a Dialog Token set to DT3+1, a Follow Up Dialog Token set toDT3, as well as an indication of time T9 (i.e., the time that the firstbroadcast ranging response message 1060 was sent by the AP). At timeT13, the STA1 receives the second broadcast ranging response message1070 and can then begin determining the RTT measurements. At time T14,the STA2 receives the same second broadcast ranging response message1070 and can begin determining its own RTT measurements. Note that ifeither the first broadcast ranging response message 1060 or the secondbroadcast ranging response message 1070 is not received by either STA1or STA2, another unicast Ranging Request Message with Dialog Token setto 0 could be sent by either STA to indicate that the respectivebroadcast ranging response message should be retransmitted by the AP. Aranging response message retransmission PPDU shall have the same DialogToken and Follow Up Dialog Token as included in ranging response message1060, but a new MAC sequence number. Another option is for either STA torestart the process by sending a unicast Ranging Request Message to theAP. Note that this mechanism has improved the medium usage for RTT by afactor of (6N)/(2N+1)˜3, where N is the number of STAs that each AP doesranging with.

It should be understood that any reference to an element herein using adesignation such as “first,” “second,” and so forth does not generallylimit the quantity or order of those elements. Rather, thesedesignations may be used herein as a convenient method of distinguishingbetween two or more elements or instances of an element. Thus, areference to first and second elements does not mean that only twoelements may be employed there or that the first element must precedethe second element in some manner. Also, unless stated otherwise a setof elements may comprise one or more elements. In addition, terminologyof the form “at least one of A, B, or C” or “one or more of A, B, or C”or “at least one of the group consisting of A, B, and C” used in thedescription or the claims means “A or B or C or any combination of theseelements.” For example, this terminology may include A, or B, or C, or Aand B, or A and C, or A and B and C, or 2A, or 2B, or 2C, and so on.

In view of the descriptions and explanations above, those of skill inthe art will appreciate that the various illustrative logical blocks,modules, circuits, and algorithm steps described in connection with theaspects disclosed herein may be implemented as electronic hardware,computer software, or combinations of both. To clearly illustrate thisinterchangeability of hardware and software, various illustrativecomponents, blocks, modules, circuits, and steps have been describedabove generally in terms of their functionality. Whether suchfunctionality is implemented as hardware or software depends upon theparticular application and design constraints imposed on the overallsystem. Skilled artisans may implement the described functionality invarying ways for each particular application, but such implementationdecisions should not be interpreted as causing a departure from thescope of the present disclosure.

Accordingly, it will be appreciated, for example, that an apparatus orany component of an apparatus may be configured to (or made operable toor adapted to) provide functionality as taught herein. This may beachieved, for example: by manufacturing (e.g., fabricating) theapparatus or component so that it will provide the functionality; byprogramming the apparatus or component so that it will provide thefunctionality; or through the use of some other suitable implementationtechnique. As one example, an integrated circuit may be fabricated toprovide the requisite functionality. As another example, an integratedcircuit may be fabricated to support the requisite functionality andthen configured (e.g., via programming) to provide the requisitefunctionality. As yet another example, a processor circuit may executecode to provide the requisite functionality.

Moreover, the methods, sequences, and/or algorithms described inconnection with the aspects disclosed herein may be embodied directly inhardware, in a software module executed by a processor, or in acombination of the two. A software module may reside in RAM memory,flash memory, ROM memory, EPROM memory, EEPROM memory, registers, harddisk, a removable disk, a CD-ROM, or any other form of storage mediumknown in the art. An exemplary storage medium is coupled to theprocessor such that the processor can read information from, and writeinformation to, the storage medium. In the alternative, the storagemedium may be integral to the processor (e.g., cache memory).

Accordingly, it will also be appreciated, for example, that certainaspects of the disclosure can include a computer-readable mediumembodying a method for broadcasting ranging messages (i.e., rangingrequest messages and/or ranging response messages), as discussed abovewith reference to FIGS. 2A-5.

While the foregoing disclosure shows various illustrative aspects, itshould be noted that various changes and modifications may be made tothe illustrated examples without departing from the scope defined by theappended claims. The present disclosure is not intended to be limited tothe specifically illustrated examples alone. For example, unlessotherwise noted, the functions, steps, and/or actions of the methodclaims in accordance with the aspects of the disclosure described hereinneed not be performed in any particular order. Furthermore, althoughcertain aspects may be described or claimed in the singular, the pluralis contemplated unless limitation to the singular is explicitly stated.

What is claimed is:
 1. A method performed by an access point of awireless local area network (WLAN), the method comprising: receiving, bythe access point, a first ranging request message from a first device ona channel of the WLAN, wherein the first ranging request messageincludes a device identifier of the first device; monitoring, by theaccess point, the channel of the WLAN for a second ranging requestmessage from a second device, wherein the second ranging request messageincludes a device identifier of the second device; in response toreceiving the second ranging request message from the second device,combining, by the access point, the device identifier of the firstdevice, first timing information associated with the first rangingrequest message, the device identifier of the second device, and secondtiming information associated with the second ranging request messageinto a single ranging response message, wherein the first and secondtiming information are for determining round trip time (RTT)measurements, by the first and second devices, respectively; andbroadcasting, by the access point, the single ranging response messageon the channel of the WLAN.
 2. The method of claim 1, furthercomprising: beginning a response time period in response to receivingthe first ranging request message, wherein the second ranging requestmessage is received during the response time period, and whereinbroadcasting the ranging response message includes broadcasting thesingle ranging response message in response to an end of the responsetime period.
 3. The method of claim 2, wherein monitoring the channel ofthe WLAN for the second ranging request message from the second devicecomprises monitoring the channel until the end of the response timeperiod, the method further comprising: in response to not receiving anyadditional ranging request messages, including the second rangingrequest message, generating the single ranging response message toinclude the device identifier only of the first device and the firsttiming information associated only with the first ranging requestmessage.
 4. The method of claim 2, wherein the first ranging requestmessage and the second ranging request message are broadcast rangingrequest messages broadcast on the channel of the WLAN by the first andsecond devices, respectively, the method further comprising randomizingthe response time period to reduce interference with other rangingresponse messages broadcast by other access points in the WLAN.
 5. Themethod of claim 2, wherein the response time period is fixed.
 6. Themethod of claim 2, wherein the response time period is variable, themethod further comprising varying the response time period based on anactivity level of the channel of the WLAN.
 7. The method of claim 6,wherein varying the response time period comprises increasing theresponse time period in response to the activity level of the channelbeing above an activity level threshold indicating a higher level ofactivity on the channel.
 8. The method of claim 1, wherein the firsttiming information comprises a time stamp indicating a time that thefirst ranging request message was received at the access point andwherein the second timing information comprises a time stamp indicatinga time that the second ranging request message was received at theaccess point.
 9. The method of claim 1, wherein the device identifier ofthe first device is a media access control (MAC) address of the firstdevice and wherein the device identifier of the second device is a MACaddress of the second device.
 10. The method of claim 1, furthercomprising broadcasting, by the access point, a second ranging responsemessage after broadcasting the single ranging response message, whereinthe second ranging response message indicates a time that the singleranging response message was broadcast on the channel by the accesspoint.
 11. An access point for use in a wireless local area network(WLAN), the access point comprising: at least one processor; and atleast one memory coupled to the at least one processor, the at least oneprocessor and the at least one memory being configured to direct theaccess point to: receive a first ranging request message from a firstdevice on a channel of the WLAN, wherein the first ranging requestmessage includes a device identifier of the first device; monitor thechannel of the WLAN for a second ranging request message from a seconddevice, wherein the second ranging request message includes a deviceidentifier of the second device; in response to receiving the secondranging request message from the second device, combine the deviceidentifier of the first device, first timing information associated withthe first ranging request message, the device identifier of the seconddevice, and second timing information associated with the second rangingrequest message into a single ranging response message, wherein thefirst and second timing information are for determining round trip time(RTT) measurements, by the first and second devices, respectively; andbroadcast the single ranging response message on the channel of theWLAN.
 12. The access point of claim 11, wherein the at least oneprocessor and the at least one memory are further configured to directthe access point to: begin a response time period in response toreceiving the first ranging request message, wherein the second rangingrequest message is received during the response time period, and whereinbroadcasting the ranging response message includes broadcasting theranging response message in response to an end of the response timeperiod.
 13. The access point of claim 12, wherein the at least oneprocessor and the at least one memory are further configured to directthe access point to: monitor the channel of the WLAN for one or moreadditional ranging request messages, including the second rangingrequest message, until the end of the response time period; and inresponse to not receiving any additional ranging request messages,including the second ranging request message, generate the singleranging response message to include the device identifier only of thefirst device and the first timing information associated only with thefirst ranging request message.
 14. The access point of claim 12, whereinthe first ranging request message and the second ranging request messageare broadcast ranging request messages broadcast on the channel of theWLAN by the first and second devices, respectively, and wherein the atleast one processor and the at least one memory are further configuredto direct the access point to randomize the response time period toreduce interference with other ranging response messages broadcast byother access points in the WLAN.
 15. The access point of claim 12,wherein the response time period is variable, and wherein the at leastone processor and the at least one memory are further configured todirect the access point to vary the response time period based on anactivity level of the channel of the WLAN.
 16. The access point of claim15, wherein the at least one processor and the at least one memory arefurther configured to direct the access point to increase the responsetime period in response to the activity level of the channel being abovean activity level threshold indicating a higher level of activity on thechannel.
 17. The access point of claim 11, wherein the first timinginformation comprises a time stamp indicating a time that the firstranging request message was received at the access point and wherein thesecond timing information comprises a time stamp indicating a time thatthe second ranging request message was received at the access point. 18.The access point of claim 11, wherein the device identifier of the firstdevice is a media access control (MAC) address of the first device andwherein the device identifier of the second device is a MAC address ofthe second device.
 19. The access point of claim 11, wherein the atleast one processor and the at least one memory are further configuredto direct the access point to broadcast a second ranging responsemessage after broadcasting the single ranging response message, whereinthe second ranging response message indicates a time that the singleranging response message was broadcast on the channel by the accesspoint.
 20. An access point for use in a wireless local area network(WLAN), the access point comprising: means for receiving, by the accesspoint, a first ranging request message from a first device on a channelof the WLAN, wherein the first ranging request message includes a deviceidentifier of the first device; and means for monitoring, by the accesspoint, the channel of the WLAN for a second ranging request message froma second device, wherein the second ranging request message includes adevice identifier of the second device; means for combining, by theaccess point, the device identifier of the first device, first timinginformation associated with the first ranging request message, thedevice identifier of the second device, and second timing informationassociated with the second ranging request message into a single rangingresponse message in response to receiving the second ranging requestmessage from the second device, wherein the first and second timinginformation are for determining round trip time (RTT) measurements, bythe first and second devices, respectively; and means for broadcasting,by the access point, the single ranging response message on the channelof the WLAN.
 21. The access point of claim 20, further comprising: meansfor beginning a response time period in response to receiving the firstranging request message, wherein the second ranging request message isreceived during the response time period, and wherein the means forbroadcasting the ranging response message includes means forbroadcasting the ranging response message in response to an end of theresponse time period.
 22. A method performed by a device in a wirelesslocal area network (WLAN), the method comprising: transmitting, by thedevice, a first ranging request message on a channel of the WLAN,wherein the first ranging request message includes a device identifierof the device; receiving, by the device, a first broadcast rangingresponse messages broadcast on the channel by a first access point ofthe WLAN in response to the first ranging request message, wherein thefirst broadcast ranging response message comprises: the deviceidentifier of the device, first timing information associated with thefirst ranging request message, a device identifier of a second device inthe WLAN, and second timing information associated with a second rangingrequest message transmitted on the channel of the WLAN by the seconddevice; and determining a round trip time (RTT) measurement for thefirst access point based on the first ranging request message and thefirst timing information included in the first broadcast rangingresponse messages.
 23. The method of claim 22, wherein transmitting thefirst ranging request message on the channel of the WLAN comprisesunicasting the first ranging request message to the first access pointof the WLAN.
 24. The method of claim 22, wherein the first timinginformation comprises a time stamp indicating a time that the firstranging request message was received at the first access point andwherein the second timing information comprises a time stamp indicatinga time that the second ranging request message was received at the firstaccess point.
 25. The method of claim 22, wherein the device identifierof the device is a media access control (MAC) address of the device andwherein the device identifier of the second device is a MAC address ofthe second device.
 26. The method of claim 22, further comprisingreceiving, at the device, a second ranging response messages transmittedby the first access point of the WLAN, wherein the second rangingresponse message indicates a time that the first broadcast rangingresponse message was broadcast on the channel by the first access point.27. The method of claim 22, wherein transmitting the first rangingrequest message comprises broadcasting the first ranging request messageon the channel of the WLAN, the method further comprising: monitoringthe channel of the WLAN for the first broadcast ranging response messagebroadcast on the channel by the first access point of the WLAN; andmonitoring the channel of the WLAN for one or more other first broadcastranging response messages broadcast by a respective one or more otheraccess points of the WLAN in response to the first ranging requestmessage.
 28. The method of claim 27, further comprising: beginning await time period in response to broadcasting the first ranging requestmessage on the channel of the WLAN, wherein the first broadcast rangingresponse message is received during the wait time period, and whereinmonitoring the channel of the WLAN for the one or more other firstbroadcast ranging response messages comprises monitoring the channel forthe one or more other first broadcast ranging response messages until anend of the wait time period.
 29. The method of claim 28, wherein thewait time period is variable, the method further comprising varying thewait time period based on an activity level of the channel.
 30. Themethod of claim 22, further comprising repeating the broadcasting,monitoring, and determining, for each of a plurality of channels of theWLAN.